Leakage of hot combustion gases and/or cooling flows between turbomachinery components generally causes reduced power output and lower efficiency. For example, hot combustion gases may be contained within a turbine by providing pressurized compressor air around a hot gas path. Typically, leakage of high pressure cooling flows between adjacent turbine components (such as stator shrouds, nozzles, and diaphragms, inner shell casing components, and rotor components) into the hot gas path leads to reduced efficiency and requires an increase in burn temperature, and a decrease in engine gas turbine efficiency to maintain a desired power level as compared to an environment void of such leakage. Turbine efficiency thus can be improved by reducing or eliminating leakage between turbine components.
Traditionally, leakage between turbine component junctions is treated with metallic seals positioned in the seal slots formed between the turbine components, such as stator components. Seal slots typically extend across the junctions between components such that metallic seals positioned therein block or otherwise inhibit leakage through the junctions. However, preventing leakage between turbine component junctions with metallic seals positioned in the seal slots in the turbine components is complicated by the relatively high temperatures produced in modern turbomachinery. Due to the introduction of new materials, such as ceramic-matrix composite (CMC) turbine components, that allow turbines to operate at higher temperatures (e.g., over 1,500 degrees Celsius) relative to traditional turbines, conventional metallic turbine seals for use in seal slots may not be adequate.
Preventing leakage between turbine component junctions with metallic seals is further complicated by the fact that the seal slots of turbine components are formed by corresponding slot portions in adjacent components (a seal positioned therein thereby extending across a junction between components). Misalignment between these adjacent components, such as resulting from thermal expansion, manufacturing, assembly and/or installation limitations, etc., produces an irregular seal slot contact surface that may vary in configuration, shape and/or magnitude over time. Further, the seal slot contact surface may include surface irregularities or roughness, such as resulting from manufacturing limitations, thermal expansion, wear, etc., that allow air to migrate between the seal slot contact surface and the outer surface(s) of a seal positioned there against. The surface roughness of the seal slot contact surface may also vary overtime, such as resulting from thermal cyclic loading and/or wear.
Such irregularities in the seal slot contact surface allow for leakage across a seal positioned within the seal slot if the seal does not deform or otherwise conform to such irregularities. Unfortunately, many conventional metallic seals that attempt to account for such irregular seal slot contact surfaces (e.g., due to misalignment) do not adequately withstand current turbine operating temperatures. Further, many conventional metallic and non-metallic seals that do attempt to account for surface irregularities of the seal slot contact surfaces are not able to adapt to changes of the surface irregularities over time, as they typically plastically deform or detach to at least partially fill the surface irregularities.
There is a need for further turbomachinery having seal slots and seals for reducing leakage, and more particularly to turbomachinery having coated seal slot systems and methods for forming the same operable to reduce leakage between adjacent components of turbomachinery.